How would I find a spell's number ?

I want to give a class I made a certain skill but I can't find it's number...
I would appreciate it if someone could tell me,
thanks in advance.

You should be able to use slookup:
http://www.gammon.com.au/forum/?wiki=slookup

You probably need to use SSET to set the spell's slot number. Remember though that all skills are generally slot 0, and that each spell must have it's own slot number... there's a snippet floating around out there that I use on my mud which creates an immortal command called slotlist which will display for you all of your skills, spells, tongues, and weapon styles along with what slot numbers they're each using and which slot numbers are still free. It's pretty handy for this sort of thing.

Thanks for answering me guys

No problem. :)
Hope at least one of the two of us actually helped. ;)